Epidemiological and Molecular Assessment of Onchocerciasis Transmission Interruption in Historically Hyperendemic Communities of Kaduna State

Nigeria is one of the last major onchocerciasis-endemic countries yet to achieve verified transmission interruption in any focus, and rigorous epidemiological and molecular assessment of potential interruption is critical for programme transition planning. This doctoral study conducted a comprehensive transmission interruption assessment in four historically hyperendemic communities of Kaduna State that had received uninterrupted annual ivermectin treatment for over 16 years. A cross-sectional design enrolled 640 children aged 5 to 10 years who had never received ivermectin. Microfilarial prevalence was assessed by skin snip microscopy, and O-150 repeat DNA ELISA was performed on skin snips. Simulium damnosum complex vector density and infectivity were assessed by dissection and PCR over two full transmission seasons. Entomological indicators including annual transmission potential and infective larval rate were calculated. Microfilarial prevalence in the sentinel age group was below 1 percent in all four communities. Skin snip O-150 ELISA was positive in 2.1 percent of children, requiring continued monitoring. Simulium vector dissection and PCR yielded zero L3 infectivity across the two-year transmission season assessment. These combined epidemiological and entomological data approach but do not fully satisfy the WHO criteria for transmission interruption verification, specifically the serological threshold. The study proposes a three-year extended monitoring protocol incorporating molecular xenomonitoring before formal verification submission. Keywords: onchocerciasis, transmission interruption, ivermectin, Simulium, Kaduna State.